The present invention relates to a liquid cooling type projection picture tube used in a color projector.
In a conventional color projection picture tube, respective color images are produced by corresponding mnochromatic picture tubes such as a two- or three-tube picture tube. These images are projected on a projection screen to form a color image, pixels of which are combined.
A picture tube of high brightness is desired in such a projector. Since such a picture tube has a high output, the temperature of a panel is increased upon operation for a long period of time, thereby degrading the white balance of the color image projected on the screen.
In order to solve this problem in a conventional picture tube of this type, a chamber which seals a liquid therein is disposed in contact with the panel of the phosphor screen of the picture tube to dissipate heat through a heat dissipation plate by convection of the liquid. The heat dissipation plate is arranged around the sealing chamber. The above structure is described in Japanese Utility Model Prepublication Nos. 54-43926 and 55-177256.
FIG. 9 is a sectional view showing a structure of a liquid cooling type picture tube of high brightness. Referring to FIG. 9, a phosphor screen panel 1, a funnel 2, and a neck 3 constitute a bulb 4. A phosphor screen 6 is formed on the inner surface of the bulb 4, opposite an electron gun assembly 5 arranged in the neck 3. A frame-like heat dissipation plate 7 is adhered to the peripheral portion of the panel 1 through an adhesive 8. The heat dissipation plate 7 is further adhered to a transparent panel 9 through the adhesive 8. An injection port (not shown) is formed in the heat dissipation plate 7. A sufficiently degassed coolant 10 is injected in a sealing chamber 11, formed of the phosphor screen panel 1 and the transparent panel 9, so as to completely eliminate air from the sealing chamber 11. The injection port is then completely sealed with a stopper. Heat generated by the phosphor screen panel 1 of the bulb 4 can be dissipated outside the bulb 4 through the heat dissipation plate 7 by convection of the coolant 10 which is easily convected. Therefore, the surface temperature of the phosphor screen panel 1 can be limited to about 80.degree. C., thereby obtaining a stable image.
In the system described above, the coolant 10 in the sealing chamber 11 repeats expansion/contraction according to temperatures in operative/nonoperative states of the picture tube. The reference temperature of the coolant 10 varies on the basis of the operative or nonoperative temperature. If the reference temperature is based on the operative temperature, the coolant 10 contracts in the nonoperative state. However, if the reference temperature is based on the nonoperative temperature, the coolant 10 expands in the operative state. In either case, the sealing chamber 11 repeatedly receives the stress. When this stress exceeds the strength of the surface adhered by the adhesive 8 and defining the sealing chamber 11, the adhesive 8 is removed and the coolant 10 may leak. The adhesive 8 is normally a silicone-based organic adhesive having a high modulus of elasticity so as to absorb the stress as much as possible. The volume expansion of the coolant 10 upon an increase in temperature during use for a long period of time can be absorbed. Therefore, the liquid cooling structure can be achieved with a relatively simple structure.
With this construction, since the adhesive 8 is used to constitute the sealing chamber 11, bulky manufacturing equipment is required for maintaining and controlling cleanness of the surface of the heat dissipating plate 7 and the phosphor screen panel 1.